For achievement of high efficiency from a vane-type hydraulic motor, and for proper rotor vane loading, it is desirable to minimize the fluid leakage down the side of the rotor to the motor case, that is the case drain leakage. The case drain leakage can be reduced by utilizing very close operating clearances between the rotor and the stator side housing. However, this is not always a satisfactory solution since large changes in operating temperature, changes in fluid viscosity, axial loading of the motor housing, and other factors can cause galling of the rotor with the stator. This has proved to be a potentially severe problem with large hydraulic motors of the type illustrated in U.S. Pat. No. 3,782,867. In these large motors, a clearance adequate for preventing galling causes high case drain flow and improper loading of the rotor vanes. The latter in turn causes periodic high leakage across the vane tips followed by sudden loading of the rotor vane with a resultant hydraulic shock.
The present invention is directed to providing side seals in a fluid power converter to permit proper pressure loading of the rotor vanes and to provide an improved seal which has a long life and which limits case drain leakage.